Veterans “The Big Bang Theory” on CBS and “Grey’s Anatomy” on ABC were the top ratings draws for young adults Thursday, a night that saw acceptable week-2 scores for the same nets’ “Bad Teacher” and “Black Box,” respectively. NBC improved its standing on the night with the inaugural “iHeart Radio Music Awards,” which helped send Fox’s “American Idol” to a fourth-place finish in its timeslot.

According to preliminary national estimates from Nielsen, “The Big Bang Theory” (4.4/16 in 18-49, 15.7 million viewers overall) was in line with last week and more than doubled the demo score of every other Thursday series except “Grey’s Anatomy.” The net fell off quite a bit at 8:30 p.m. with “The Millers” (2.1/7 in 18-49, 9.6 million viewers overall), which was down 13% from last week, and “Two and a Half Men” (2.1/6 in 18-49, 9.2 million viewers overall) was low too. “Bad Teacher” (1.5/4 in 18-49, 6.5 million viewers overall) declined a fairly steep 29% from its premiere — though this isn’t quite as bad considering its “Two and a Half Men” lead-in was 16% lower itself. “Elementary” closed the night for CBS (1.6/5 in 18-49, 7.8 million viewers overall), matching last week’s score.

CBS won Thursday in 18-49, 25-54 and total viewers — the third straight night it has swept these categories.

At ABC, a “Grey’s Anatomy” repeat from 2007 featuring Isaiah Washington’s final appearance as a series regular (0.9/3 in 18-49, 4.1 million viewers overall) was followed by Washington’s return in a new episode at 9 (2.6/8 in 18-49, 8.7 million viewers overall). The medical drama was up 13% week to week and drew its largest overall audience since its midseason return on Feb. 27. At 10 p.m., “Black Box” (1.3/4 in 18-49, 5.4 million viewers overall) was aided by a stronger “Grey’s” lead-in, with its 13% falloff from its week-ago premiere making it the best week-2 hold for a new ABC drama this season.

At Fox, “Hell’s Kitchen” (1.6/6 in 18-49, 4.4 million viewers overall) and “American Idol” (series-low 1.5/5 in 18-49, 6.9 million viewers overall) both fell from last week, with the latter humbled to a fourth-place finish in 18-49 for the 9 o’clock half-hour. At 9:30 p.m., “Surviving Jack” (1.0/3 in 18-49, 3.9 million viewers overall) was in line with the previous week.

NBC’s three-hour “iHeart Radio Music Awards” (1.7/5 in 18-49, 5.5 million viewers overall) roughly doubled the net’s prior week’s average with series programming and was up 31% from the net’s non-sports Thursday average this season (1.3). The net finished second on the night in 18-49 and ranked No. 1 in the 10:30 p.m. half-hour. Though a good number for a first-year kudocast, Thursday’s show delivered about half what ABC did last spring with its established “Billboard Music Awards.”

“The iHeart Radio Music Awards,” which has been promoted for months on Clear Channel radio stations, featured performances by artists including Pharrell Williams, Ed Sheeran and Thirty Seconds to Mars.

At CW, “The Vampire Diaries” (0.7/3 in 18-49, 1.8 million viewers overall) was low, but managed to match its week-ago 18-34 score (0.8/3), and “Reign” (0.5/2 in in 18-49, 1.4 million viewers overall) followed with a week-to-week gain in 18-34 (to 0.5/2). In both total viewers and women 18-34 (1.0/3), this was CW’s best Thursday in six weeks.